Auto merge of #106916 - lukas-code:overlapping-substs, r=estebank

Remove overlapping parts of multipart suggestions

This PR adds a debug assertion that the parts of a single substitution cannot overlap, fixes a overlapping substitution from the testsuite, and fixes rust-lang/rust#106870.

Note that a single suggestion can still have multiple overlapping substitutions / possible edits, we just don't suggest overlapping replacements in a single edit anymore.

I've also included a fix for an unrelated bug where rustfix for `explicit_outlives_requirements` would produce multiple trailing commas for a where clause.

Author: bors